1. Field of the Invention
The present invention generally relates to the art of forming a number of stitches on a single work sheet, or two or more work sheets superposed on each other, by moving the work sheet(s) relative to a stitch-forming device including a sewing needle, according to sewing data, and thereby producing a desired sewing pattern consisting of the thus formed stitches. In particular, the present invention relates to the art of modifying the sewing data.
2. Related Art Statement
There is known a sewing machine having (a) a work-holding device for holding one or more work sheets, (b) a stitch-forming device including a sewing needle, for forming stitches on the work sheet(s), and (c) a displacing device for displacing the work-holding device and/or the stitch-forming device, relative to each other. The displacing device includes a drive source, such as a pulse motor, which is controllable with respect to rotation amounts, and the displacing device is controlled according to sewing data so as to operate in synchronism with the operation of the stitch-forming device.
Sewing data define the relative positions of the stitch-forming device and the work-holding device, i.e., the relative positions of the needle as part of the stitch-forming device and the work sheet(s) held by the work-holding device, in a two-dimensional coordinate system, i.e., on a coordinate plane. Generally, an orthogonal X-Y coordinate plane defined by an X axis and a Y axis perpendicular to each other (hereinafter, referred to simply as an "X-Y coordinate plane") is used, but other kinds of coordinate planes such as a polar coordinate plane may be used to form a special sewing pattern. For easier understanding, the following statement will be made on the assumption that sewing data are prepared using an X-Y coordinate plane.
The displacing device of the sewing machine is required to displace the stitch-forming device and/or the work-holding device, relative to each other, on an X-Y coordinate. Therefore, the displacing device may be (a) a device which displaces the stitch-forming device relative to the work-holding device along each of the X and Y axes of the X-Y coordinate plane; (b) a device which displaces the stitch-forming device relative to the work-holding device along one of the X and Y axes and displaces the work-holding device relative to the stitch-forming device along the other of the X and Y axes; or (c) a device which displaces the work-holding device relative to the stitch-forming device along each of the X and Y axes. Generally, the last device (c) is employed, that is, the displacing device of the sewing machine displaces the work sheet(s) held by the work-holding device, relative to the needle as part of the stitch-forming device, along each of the X and Y axes. However, it is most understandable to assume that the first device (a) is employed, that is, the displacing device of the sewing machine displaces the stitch-forming device relative to the work-holding device along each of the X and Y axes so that the needle is moved relative to the work sheet(s). Since the first and last devices (a), (c) are mathematically equivalent to each other, the following statement will be made on the assumption that a sewing needle is moved relative to a work sheet(s).
Sewing data contain, at least, stitch-position defining data defining a number of stitch positions where a sewing needle penetrates a work sheet(s) held by a work-holding device. Stitch-position defining data may be (a) sets of stitch-position data each of which directly represents the x and y coordinates of a corresponding one of the stitch positions on the X-Y coordinate plane; (b) data which indirectly represent the stitch positions, for example, data representing the respective distances of movement of the needle from each stitch position to the following stitch position along the X and Y axes; or (c) data for use as a basis for calculating the x and y coordinates of each stitch position, for example, combination of (c1) data representing an embroidery area and (c2) data representing the density of stitches to be formed in the embroidery area. In almost all cases, the stitch-position defining data additionally contain control data to move the stitch-forming device relative to the work-holding device while the needle is stopped. When the operation of the displacing device is controlled in synchronism with the operation of the stitch-forming device according to the sewing data, a group of stitches are formed, on the work sheet(s), at the respective stitch positions in accordance with the sewing data, so that a sewing product having a sewing pattern consisting of the group of stitches are obtained.
Thus, sewing data provide part of a control program which additionally includes various auxiliary data such as (a) control data to start and stop the operation, and change the rotation speed, of a drive motor as a drive source of the stitch-forming device; and (b) control data to cut a sewing thread carried by the needle, after completion of a sewing operation.
A sewing pattern formed by the sewing machine may be (a) a stitch line consisting of stitches formed on a single straight or curved line; (b) a stitch pattern consisting of stitches which are formed essentially along a single straight or curved line and at least a part of which are formed at positions away from the single line; or (c) an embroidery pattern consisting of dense or coarse stitches filling an area bounded by a closed outline.
In many cases, the work-holding device holds a plurality of work sheets superposed on each other. However, in the case where a stitch pattern or an embroidery pattern is formed, a single work sheet may be held by the work-holding device. The work sheet(s) may be a cloth sheet(s), a leather sheet(s), a soft-resin sheet(s), or other kinds of sheet(s).
When a sewing machine is controlled according to sewing data, a sewing pattern in accordance with the sewing data is formed on a work sheet(s) as described above. However, the sewing pattern may not be formed at an appropriate or accurate position on the work sheet(s). The relative position of the stitch-forming device and the work-holding device in the sewing machine contains the errors of machining of individual parts of the two devices and the errors of assembling of the two devices from their parts. Therefore, even if the work sheet(s) is(are) held accurately in position by the work-holding device, some relative-positional error will remain between the work sheet(s) and the needle of the stitch-forming device. If a sewing pattern is formed using sewing data for which the above relative-positional error has not been taken into consideration, the sewing pattern formed is located out of position from a prescribed, accurate position on the work sheet(s).
Sewing data may be produced by (a) an exclusive-use sewing-data producing device which does not have the stitch-forming function (hereinafter, referred to as the "exclusive sewing-data producing device"), or (b) a sewing machine which has the sewing-data-producing function in addition to the stitch-forming function.
In the former case (a), sewing data may be produced by (a1) drawing, on a display of a data processing device such as a personal computer, a figure corresponding to a sewing pattern itself, or a straight or curved line or an embroidery area each defining a sewing pattern, and processing the drawn figure; by (a2) inputting various data into a data processing device through a data input device such as a keyboard and processing the input data; or (a3) reading the relative positions of a paper pattern corresponding to a work sheet(s), relative to a pointer corresponding to a sewing needle, and processing the read relative-position data. Meanwhile, in the latter case (b), sewing data may be obtained by having a work sheet(s), or a pattern sheet corresponding to the work sheet(s), held by a work-holding device of the sewing machine and reading the relative positions of the work sheet(s) or pattern paper relative to a sewing needle as a pointer of the sewing machine. To this end, an operator has the work sheet(s) or paper pattern held accurately in position on a sewing frame of the work-holding device. Thus, the sewing data produced on (b) the sewing machine are adapted to the actual position of the sewing frame thus serving as a work-positioning reference member.
Hereinafter, first, there will be explained the first case (a) where sewing data are produced using an exclusive sewing-data producing device. In this case, normally, sewing data are prepared using a theoretical X-Y coordinate plane which a sewing machine is designed to have.
However, the sewing machine has, in addition to the above theoretical X-Y coordinate plane, an actual X-Y coordinate plane defined by the actual relative position of a stitch-forming device and a displacing device thereof.
The displacing device of the sewing machine includes (1) an X-axis displacing device for displacing the stitch-forming device in a positive and a negative direction along a first axis corresponding to the X axis of the theoretical X-Y coordinate plane, and (2) a Y-axis displacing device for displacing the stitch-forming device in a positive and a negative direction along a second axis corresponding to the Y axis of the theoretical X-Y coordinate plane. It is not essential but very convenient to regard, as the origin of the actual X-Y coordinate plane, the position of the needle at the time when the needle is positioned at the respective origins of the first and second axes, respectively.
However, in almost all cases, the respective origins of the first and second axes of the X-axis and Y-axis displacing devices are located more or less out of position from the origin of the theoretical X-Y coordinate plane, because of the cumulative errors of machining and assembling of the individual parts of the X-axis and Y-axis displacing devices and the stitch-forming device. For the same reason, the first and second axes of the X-axis and Y-axis displacing devices are slanted more or less from, i.e., are not parallel to, the X and Y axes of the theoretical X-Y coordinate plane, respectively. Consequently, the actual X-Y coordinate plane is translated from, and rotated from, the theoretical X-Y coordinate plane.
Fortunately, even in the case where sewing data are prepared using the theoretical X-Y coordinate plane, the sewing data can be used on the actual X-Y coordinate plane of the sewing machine, as if there were no translation or no rotation of the actual X-Y coordinate plane from the theoretical X-Y coordinate plane. Therefore, it can be said that there is no translation or no rotation of the actual X-Y coordinate plane from the theoretical X-Y coordinate plane.
However, there may remain some amount of translation and/or some amount of rotation of the work-holding device with respect to the actual X-Y coordinate plane, i.e., or the displacing device defining the actual X-Y coordinate plane, for the same reason as explained above. Since a work sheet(s) is(are) held accurately in position on the work-holding device by using a work-positioning reference member such as a sewing frame of the work-holding device, the relative-positional error of the work-holding device with respect to the displacing device directly results in forming a sewing pattern more or less out of position on the work sheet(s).
Next, there will be explained the second case (b) where sewing data are produced by a sewing machine. In this case, as previously described, the sewing data produced are adapted to the actual position of the work-positioning reference member of the work-holding device. Therefore, by adjusting (1) the actual position of the work-positioning reference member relative to the work-holding device and/or (2) the actual position of the work-holding device relative to the displacing device, the relative-positional error of the work-positioning reference member relative to the displacing device can be eliminated in advance before sewing data are produced. The thus adjusted sewing machine enables sewing data to be prepared using the actual X-Y coordinate plane of the sewing machine. The sewing data thus prepared on the sewing machine using the actual X-Y coordinate plane thereof are equivalent to the sewing data produced by the exclusive sewing-data producing device using the theoretical X-Y coordinate plane, so that the former sewing data can be used in place of the latter sewing data without needing any modification.
On the other hand, in the case where the actual position of the work-holding device is not adjusted in advance before sewing data are produced, the sewing data produced are adapted to the work-positioning reference member located out of position relative to the actual X-Y coordinate plane of the sewing machine. Thus, the sewing data contain a relative-positional error with respect to the actual X-Y coordinate plane of the sewing machine. Therefore, if the sewing data are used on another sewing machine, a sewing pattern is formed, on the work sheet(s), out of position by an amount corresponding to the difference of (1) the relative-positional error of the first sewing machine on which the sewing data are produced and (2) that of the second sewing machine on which the sewing data are used.
For the reasons explained above in detail, a sewing pattern formed by a sewing machine using the sewing data produced by the exclusive sewing-data producing device, may not be located at an appropriate or accurate position on a work sheet(s).
In contrast, when a sewing pattern is formed by a sewing machine using the sewing data produced by the same sewing machine, no problem arises. However, when the sewing data are used on another sewing machine, the same problem arises.
In some cases, the problem that a sewing pattern is not formed at an accurate position on a work sheet(s) does not provide any adverse effect. However, for example, in the case where a sewing pattern is formed for attaching a pocket to a garment or in the case where a stitch line or a stitch pattern is formed along the edges of a work sheet(s), the above problem results in greatly lowering the quality of a sewing product. This problem is exaggerated in the particular case where an elongate sewing pattern is formed, e.g., along the longitudinal edges of a belt.
Meanwhile, the production of a number of identical sewing products in a short period of time may be carried out by concurrently operating a plurality of sewing machines belonging to a sewing system. In this method, the sewing data produced by an exclusive sewing-data producing device may be input into each of the sewing machines, or the sewing data produced by using one of the sewing machines may be input into each of the other sewing machines. In either case, however, the sewing products produced by the different sewing machines suffer from the problem that the sewing patterns are formed at different positions on the different products.
If each of the sewing machines is designated to produce sewing data exclusive therefor and the produced sewing data are used on that sewing machine only, no problem arises. In this case, however, it is required to produce the same number of batches of sewing data as the number of the sewing machines, and the production efficiency of the sewing products is greatly lowered.